715 Original Paper Cell Physiol Biochem 2011;28:715-724 Accepted: September 19, 2011 Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology and Biochemistr and Biochemistr and Biochemistr and Biochemistr and Biochemistry Copyright © 2011 S. Karger AG, Basel Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com © 2011 S. Karger AG, Basel 1015-8987/11/0284-0715$38.00/0 Accessible online at: www.karger.com/cpb CFTR and TMEM16A are Separate but Functionally Related Cl - Channels Jiraporn Ousingsawat # , Patthara Kongsuphol # , Rainer Schreiber and Karl Kunzelmann Institut für Physiologie, Universität Regensburg, Regensburg, # JO and PK share first authorship Karl Kunzelmann Institut für Physiologie, Universität Regensburg Universitätsstraße 31, 93053 Regensburg (Germany) Tel. +49 (0)941 943 4302, Fax +49 (0)941 943 4315 E-Mail karl.kunzelmann@vkl.uni-regensburg.de Key Words Ca 2+ activated Cl - currents  CaCC  TMEM16A  CFTR  Cystic fibrosis  CF Abstract Previous reports point out to a functional relationship of the cystic fibrosis transmembrane conductance regulator (CFTR) and Ca 2+ activated Cl - channels (CaCC). Recent findings showing that TMEM16A forms the essential part of CaCC, prompted us to examine whether CFTR controls TMEM16A. Inhibition of endogenous CaCC by activation of endogenous CFTR was found in 16HBE human airway epithelial cells, which also express TMEM16A. In contrast, CFBE airway epithelial cells lack of CFTR expression, but express TMEM16A along with other TMEM16- proteins. These cells produce CaCC that is inhibited by overexpression and activation of CFTR. In HEK293 cells coexpressing TMEM16A and CFTR, whole cell currents activated by IMBX and forskolin were significantly reduced when compared with cells expressing CFTR only, while the halide permeability sequence of CFTR was not changed. Expression of TMEM16A, but not of TMEM16F, H or J, produced robust CaCC, which that were inhibited by CaCCinh- A01 and niflumic acid, but not by CFTRinh-172. TMEM16A-currents were attenuated by additional expression of CFTR, and were completely abrogated when additionally expressed CFTR was activated by IBMX and forskolin. On the other hand, CFTR- currents were attenuated by additional expression of TMEM16A. CFTR and TMEM16A were both membrane localized and could be coimmuno- precipitated. Intracellular Ca 2+ signals elicited by receptor-stimulation was not changed during activation of CFTR, while ionophore-induced rise in [Ca 2+ ] i was attenuated after stimulation of CFTR. The data indicate that both CFTR and TMEM16 proteins are separate molecular entities that show functional and molecular interaction. Introduction The cystic fibrosis transmembrane conductance regulator (CFTR) is regarded as a cAMP/PKA/ATP- regulated Cl - channel that also controls the function of other membrane proteins [1]. Apart from the well examined effects of CFTR on epithelial Na + conductance, it has also been reported earlier that CFTR inhibits